The heart of man finds it difficult to believe that so great a treasure as the Holy Ghost is gotten by the mere hearing of faith. The hearer likes to reason like this: Forgiveness of sins, deliverance from death, the gift of the Holy Ghost, everlasting life are grand things. If you want to obtain these priceless benefits, you must engage in correspondingly great efforts. And the devil says, "Amen."
Commentary on the Epistle to the Galatians, chapter 3